Radio frequency identification (RFID) technology is becoming increasingly important for logistics concerns, material handling and inventory management in retail stores, warehouses, distribution centers, buildings, and like controlled areas. An RFID system includes an RFID reader, also known as an RFID interrogator, which has a radio frequency (RF) transceiver and an antenna that emits RF waves generated by the transceiver over a coverage range. The RFID system also includes an RFID tag, which is a small transponder having a tag antenna, and is typically placed on, or associated with, an item, e.g., a product or its packaging, to be tracked. When the RFID tag of the item is located in the coverage range of the reader and receives the RF waves, the tag is activated. Once the tag has been activated, the tag sends RF waves containing identifying data back to the reader, thereby identifying the item to which the tag is attached, or with which the tag is otherwise associated. One form of the RFID tag modifies and reflects the waves emitted by the reader, using the modified and reflected waves to communicate with the reader, in a backscatter process. In another form of the RFID tag, the tag emits an RF signal which is detected by the reader.
There are three basic types of RFID tags. A passive tag receives all the energy required for its operation from the RF waves generated by the reader, and reflects some of the received energy as the passive tag communicates with the reader. A semi-active (also referred to sometimes as semi-passive) tag is powered by an on-board battery, but still communicates by reflecting some of the energy radiated by the reader. A reflected signal is modulated by changing the impedance of the tag antenna, thereby changing the ratio between the absorbed energy and the reflected energy. Since, in most cases, the coverage range of the RFID reader is limited by the amount of energy needed to power the passive tags, semi-active tags usually have a significantly larger coverage range even when operating the same reader under the same conditions since the tag does not need to derive its operating power from the energy radiated by the reader. An active tag is essentially a fully functional radio, with on-board power and a stand-alone transceiver. An active tag can be read at an even greater distance or coverage range from a reader as compared, for example, to a passive or a semi-active tag.
The RFID system is often used in an inventory monitoring application. For example, in order to take inventory of RFID-tagged items in a retail store, it is known for store personnel with handheld RFID readers to manually make rounds through an inventory area of the store. Since this manual inventory-taking process relies on store personnel to physically walk through the entire inventory area to read each RFID-tagged item over a significant amount of time, it is not very efficient, or accurate, and, in practice, may not be frequently performed.
To automate and improve the manual inventory-taking process, it is also known to arrange a plurality of RFID readers at fixed locations throughout the inventory area, and then, to allow the readers to automatically read whatever RFID-tagged items are in their respective coverage ranges. To help better locate the RFID readers and, in turn, the RFID-tagged items that the RFID readers “see”, one can use one or more “beacon tags” or “fiducial tags”. The beacon/fiducial tags are RFID tags that are not attached or associated with any inventory item, but instead, are permanently placed in known locations throughout the inventory area, e.g., around a door frame, or in walls, or a floor, or a ceiling, of a building, or on shelves and racks. Since the locations of the beacon/fiducial tags are fixed and known, the RFID system may determine the location of any particular RFID reader whose location is being determined based on which beacon/fiducial tags are detected by the RFID reader. As another example, it is known to enable an RFID reader to determine its own location by reading RFID-tagged items in its coverage range. As still another example, it is known to utilize a satellite-based global positioning system (GPS) technology to determine the locations of RFID readers.
As advantageous as such automatic inventory-taking systems have been, the deployment of the RFID readers may not optimally cover the inventory area. There may be duplication in RF coverage in one or more zones, and there may be gaps in the RF coverage in one or more other zones. Even if the deployment of the RFID readers does optimally cover the inventory area, inventory area layouts may change, one or more of the RFID readers may be moved and sometimes to random locations, the RFID-tagged items may be moved, and the GPS technology may not work well indoors. One or more of such actions or events will defeat any assurance that the RFID system will have adequate and contiguous RF coverage over the entire controlled inventory area. Knowing the exact location of each RFID reader, despite the occurrence of any such actions/events, improves manufacturing and distribution efficiency, and translates to a more effective competitive presence in the marketplace.
Accordingly, there is a need to efficiently and non-randomly deploy RFID readers in a controlled area to insure contiguous and optimal RF coverage throughout the entire controlled area, that is, not too many readers that might result in duplication of RF coverage, and not too few readers that might result in gaps or holes in the RF coverage, and, once the RFID readers are deployed, to dynamically monitor the locations of the RFID readers and/or of the RFID-tagged items in the controlled area to maintain the contiguous and optimal RF coverage, and to dynamically report on the status, or change in status, of such RF coverage, and to guide a user to deploy new RFID readers, or to redeploy one or more of the existing RFID readers to again achieve contiguous and optimal RF coverage in case any of the above-described changing actions/events occur.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.